Noninvasive positive pressure ventilation (NIPPV) is currently being used to improve the quality and extend the life of patients with severe chronic lung disease. NIPPV provides ventilatory muscle rest, resulting in improved gas exchange and, in some studies, improved pulmonary function tests. NIPPV has also been shown to result in increased weight, energy and alertness. NIPPV is now being used clinically as palliative treatment or as a bridge to transplantation in children with chronic lung disease, particularly cystic fibrosis. However, its long-term effects on quality of life, pulmonary function, exercise tolerance and breathing during sleep have not been assessed. We hypothesized that providing NIPPV to patients with advanced, but not terminal, chronic lung disease would reduce their work of breathing resulting in weight gain, improve gas exchange, lessen excessive daytime sleepiness, and result in improved quality of life. We propose to offer NIPPV during sleep to patients with moderate chronic lung disease, such as those with an FEV1 of 40 - 60% predicted. The patients will have overnight polysomnography, pulmonary function testing, exercise testing, calorimetry, and a quality of life questionnaire at the beginning of the study and after 3 and 6 months on NIPPV. Patients who refuse NIPPV or who cannot tolerate it will be used as the control group. Our protocol is designed to systematically study the long-term effects of NIPPV in patients with chronic lung disease. Providing nocturnal ventilatory support to patients before they develop severe chronic lung disease may improve the nutritional balance and quality of life of these patients.